In a DC electric arc furnace the melt in the furnace hearth is connected with the arc power source, usually anodically, to power the arc formed between the melt and an arcing electrode which is also connected to that power source, usually cathodically, to thereby power the arc.
For the melt connection the prior art has proposed the use of an elongated metal connector having inner and outer ends and a refractory enclosure for that connector and exposing its inner end for contact with and melting by the melt in the furnace hearth, cooling means being provided externally of the hearth for cooling the connector between its inner and outer ends for removing heat from the connector at a rate preventing it from melting throughout its length to its outer end. This permits the power connection to be made to that outer end.
In very rudimentary forms, the general concept of DC arc furnace melt connections have been suggested by the Bowman U.S. Pat. No. 3,789,127 and the Valchev et al U.S. Pat. No. 3,835,230, nether of which disclose any details required for practical commercial applications. Such details are disclosed by the Stenkvist U.S. Pat. No. 3,997,712 and by the Anderson Patent Application Ser. No. 744,423, both assigned to the assignee of the present application.
The Stenkvist patent discloses the refractory enclosure for the metal melt connector as comprising a unit on the outside of the hearth, specifically exemplified as having a curvature permitting the outer end of the metal connector to be positioned above the melt level of the furnace hearth. The Anderson patent application describes a simplification wherein the melt connector with its refractory enclosure is made to extend vertically downwardly from the melt in the furnace hearth with the advantage, among others, that if carbon-oxide gases form in the molten part of the melt connector, these gases can escape upwardly into the melt in the hearth so as to become lost in the furnace atmosphere above the melt. In this way such gases are prevented from becoming entrapped in the molten part of the melt connector and possibly introducing an explosion hazard.
It is desirable for the melt connector and its refractory enclosure to be made as short as is compatible with keeping the outer end portion of the connector safely unmelted. One important factor that must be considered is the rate of heat exchange via the interface formed between the melted and unmelted portions of the melt connector.